Present-day techniques for manufacturing equipment intended for data processing are making ever greater use of compact circuits which enable the size of such equipment to be considerably reduced. These compact circuits are often produced in the form of printed circuits which are assembled together in a number of layers of electrical connecting panels and which may or may not be provided with electronic components which are normally formed by integrated circuits contained in housings. With the object of producing circuits of even higher performance and of grouping them into a space which, relatively speaking, is even smaller, manufacturers have been led to use tiny integrated circuit wafers, generally known as chips, in place of integrated circuits mounted in housings. The wafers are mounted on substrates having numerous conductors distributed on a number of levels. The levels are spaced from each other by insulating layers, except at certain predetermined points where conductive pillars provide electrical connections between conductors situated on different levels.
Such substrates are generally produced by means of screen-printing apparatus which deposits an alternating series of conducting and insulating layers on an electrically insulating carrier, of alumina for example. Each layer is formed by applying a pasty material, having a configuration of openings corresponding to that of the layer to be produced. After each layer has been applied, the carrier is removed from the screen-printing apparatus and placed in a high-temperature oven which solidifies the layer to form an insulating or metallic layer which adheres strongly to the carrier or the previous layer. To provide electrical connections between conductors situated at different levels, it is essential to position with extreme accuracy the screens which are successively fitted into the apparatus to enable accurate deposition of the layers. The layer receiving carrier must be positioned with equal accuracy relative to the screens each time it is inserted in the apparatus.
For these purposes, in the prior art each screen in mounted in a frame having two bores which fit over two pins in the screen printing apparatus. The screen can be shifted within the frame to allow a pattern of openings in the screen to be very accurately positioned relative to the two bores. Thereby, when the frames are inserted successively into the screen-printing apparatus, various opening patterns in the screens mounted in these frames are exactly positioned with respect to the two pins.
In screen-printing apparatus produced hitherto, these two pins are attached to a horizontal plate and the pasty material is applied through the pattern of openings in the screen inserted in the apparatus by a blade. The blade is mounted on guide means attached to the plate so it is able to slide horizontally in a straight line. To allow an operator to gain access to this blade, to clean it for example, the plate is mounted to pivot about a horizontal shaft that extends perpendicular to the blade direction of movement.
Such apparatus is also fitted with a movable carriage on which the carrier which is to receive a layer is positioned. The carriage can be moved parallel to the plane of a screen previously inserted in the apparatus to enable the carrier positioned on the carriage to be brought underneath the pattern of openings in the screen.
However, such screen-printing apparatus has certain deficiencies because it is not possible to position the carriage under the screen with great accuracy. In addition, hinging of the plate on a horizontal shaft necessarily introduces some play, which prevents screens mounted on the two pins on the plate from being accurately positioned in relation to fixed parts of the apparatus.
Because the insulating layers which separate the conductor layers of the substrate are extremely thin, it has been found necessary, to overcome cross-talk between conductors on different layers, to arrange the conductors in such a way that the conductors lie practically parallel to one another on each individual level. The conductors on immediately adjacent levels extend perpendicular to each other. Hence, the patterns of openings in the screens which are successively inserted in the screen-printing apparatus consist, in essence, of lines which are substantially parallel to one another. These lines, when the corresponding screen is positioned in the apparatus, are orientated virtually either parallel or perpendicular to the direction of blade movement. However, in cases where the lines lie perpendicular to the blade movement direction, it becomes increasingly difficult to obtain on the carrier or on the insulating layer deposited previously, a deposit of pasty material which exactly follows the outline of the pattern of openings as the width of these lines becomes very small, that is to say less than a few hundred microns.